Marine invasions have been identified in virtually all regions of the
world, yet relatively few introductions have been detected in the Tropics. This
has been attributed at least in part to an increase in intrinsic native community
resistance at lower latitudes resulting from strongly interacting food webs in
high(er) diversity systems. However, recent evidence from surveys in Australia
and elsewhere indicate that tropical systems are also susceptible to invasions,
though detection ability may be constrained by taxonomic limitations. Preliminary
analyses of data from surveys designed to detect introduced species do not
support a pattern of decreased invasion success in higher diversity systems but
do indicate a strong latitudinal gradient at the mesoscale of Australia. This cannot
be attributed to disparities in search effort (controlled for by consistency in
survey effort) or taxonomic knowledge. The original hypothesis of a decreased
relative susceptibility of tropical versus temperate biota to invasions may remain
viable, but be scale dependent. Additional confounding factors may include differing
vector strengths and availability of source bioregions.